On the interference of J(HH) modulation in HSQMBC-IPAP and HMBC-IPAP experiments

The effects of phase modulation due to homonuclear proton-proton coupling constants in HSQMBC-IPAP and HMBC-IPAP experiments are experimentally evaluated. We show that accurate values of small proton-carbon coupling constants, ⁿJ_CH, can be extracted even for phase-distorted cross-peaks obtained from a selHSQMBC experiment applied simultaneously on two mutually J-coupled protons. On the other hand, an assessment of the reliability of ⁿJ_CH measurement from distorted cross-peaks obtained in broadband IPAP versions of equivalent HMBC and HSQMBC experiments is also presented. Finally, we show that HMBC-COSY experiments could be an excellent complement to HMBC for the measurement of small ⁿJ_CH values.